Double walled cryogenic vessel

ABSTRACT

1,180,094. Storing liquefied gases. CHICAGO BRIDGE &amp; IRON CO. 30 March, 1967 [10 Aug., 1966], No. 14623/67. Heading F4P. A spherical vessel for storing liquefied gases under pressure comprises a double-walled vessel, the space 16 between the double walls being pressurized (it may also be filled with powdered insulant) thereby enabling the inner wall 13 to be of lighter construction as it carries only the weight of liquid L without being stressed by the superimposed pressure in the space U. In the illustrated embodiment gas from space U is led by pipe 17 to a heat exchanger 19 whence it permeates through the walls of a porous pipe 18 into the space 16; the expansion joint 23 is to reduce the stresses on the wall 11.

Oct. 22, 1968 D. T. LUSK 3,406,526

DOUBLE WALLED CRYOGENIC VESSEL Filed Aug. 10, 1966 POROUS cazvowr I United States Patent 3,406,526 DOUBLE WALLED CRYOGENIC VESSEL Dudley T. Lusk, Westmont, lll., assignor to Chicago Bridge & Iron Company, Oak Brook, 11]., a corporation of Illinois Filed Aug. 10, 1966, Ser. No. 571,565 7 Claims. (Cl. 6250) ABSTRACT OF THE DISCLOSURE A double walled tank for the storage of cryogens where the pressure in the ullage space in the inner tank is counteracted by a pressure maintained in the space between the inner tank and the outer tank so that the inner tank can be designed to withstand the forces created by the weight of the stored liquid only without considering the force created by the ullage pressure and designing the outer tank to withstand the forces created by the weight of the inner tank and the pressure in the annulus.

This invention relates to vessels for the storage of cryogens such as liquid nitrogen and liquid oxygen.

In the storage of liquefied, normally gaseous materials, it is necessary to provide a tank or other vessel that possesses the ability to maintain the liquid at the proper temperature and pressure. In manufacturing and erecting such structures, consideration of structural design and material expense are of paramount importance. At the present time, cryogens are commonly stored in high pressure, double walled spherical tanks.

Generally, such tanks employ an inner spherical vessel of stainless steel, or other material of comparable expense, which will retain the notch toughness, ductility, tensile strength and other properties necessary for the storage of liquefied gases at cryogenic temperatures. The inner vessel is suspended inside an outer spherical shell or vessel thereby creating an annulus between the two vessels. Some such tanks require a superimposed ullage pressure to facilitate the removal of stored material when desired. Consequently, common practice has been to design the inner vessel to have walls of sufiicient thickness to withstand the combined forces of the weight of the stored liquid and the superimposed ullage gas pressure.

In the conventional design of such structures, the inner vessel is necessarily made of either a stainless steel type 304 costing approximately $O.50/lb., an aluminum alloy costing approximately $0.50/lb. or 9% nickel steel at approximately $0.35/lb. The outer tank is usually a mild carbon steel costing approximately $0.07/lb.

In the storage of liquid nitrogen with a ullage gas pressure of 325 p.s.i. in a vessel having a 32 diameter inner sphere and using conventional design methods, the inner sphere would have to be approximately 1.75" thick and the outer sphere approximately .25" thick.

With the subject invention, the ullage space of the inner sphere is allowed to communicate with the annulus between the inner and outer spheres so that as the ullage pressure acting on the inner surface of the inner sphere increases, it will be met by an equal and opposite force acting on the outer surface of the inner sphere.

Although, in most instances, optimum conditions will be achieved when the pressure acting on the outer surface of the inner sphere is equal to the ullage pressure, it may in some instances be preferred to have the pressure in the annulus less or greater than the ullage pressure. Therefore, although reference will be made hereinafter to the equal pressure situation only, it is understood that the scope of this invention includes all embodiments where the pressure in the annulus exceeds the ambient pressure.

By maintaining equal pressure on either side of the ice inner sphere in accordance with the principles disclosed herein, it is only necessary to provide an inner sphere having walls of a thickness sufficient to support the weight of the stored material, which, when referred to hereinafter, will include a reasonable safety factor, and allowance for miscellaneous hardware. To accommodate the increased pressure on the inner surface of the outer sphere, the thickness of the walls of the outer sphere is increased. The increase in material cost for the outer sphere, however, is more than offset by savings achieved by using less of the more expensive inner sphere material. The amount of savings realized will, of course, depend on the cryogen stored and the required ullage pressure.

In the subject invention, the inner sphere is designed to support the weight of the liquid to be stored. A conduit near the top of the inner sphere connects the ullage space of the inner sphere with the annulus between the inner and outer spheres.

Because the annulus is normally filled with a granular type of insulation material, it is an important element of the present invention that conduit means be provided that will not only distribute the vapor from the ullage space evenly throughout the annulus, but will prevent any of the insulation from being carried back into the inner sphere when the cycle is reversed, e.g., when the tank is being emptied. Since it is preferred that the outer sphere not be subjected to temperatures below 20 F., it is also an object of the present invention to provide a heat exchanger, if required due to operating conditions, in the line between the inner sphere and the annulus to warm the vapor to ambient temperature before entry into the annulus.

Referring to the drawing:

FIGURE 1 is a cross-sectional elevation of a cryogenic storage vessel made in accordance with the present invention.

FIGURE 2 is a cross-sectional view of a heat exchanger of the type to be used with the present invention.

In FIGURE 1 is shown a vessel 10 designed for the storage of liquefied, normally gaseous materials L. The vessel 10 is comprised of an outer sphere 11 supported by columns 12. Inner sphere 13 is shown inside outer sphere 11. Annulus 16 is filled with insulation 22 (only partially shown) which insulation may be of the granular type. Inner sphere 13 is fixed in positionv by means of support rods 14. Above liquid L stored in inner sphere 13 is ullage space U containing the vaporized stored material or other gas under pressure. The pressure in ullage space U is determined by the requirements necessary for eflicient storage and removal of liquid L. The force created by the pressure of the gas in ullage space U is shown as P and the weight or pressure of the liquid is shown as P Emanating from ullage space U is line 17 through which gas from ullage space U ultimately passes to annulus 16. Line 17 extends through annulus 16 and the outer sphere 11 into the ambient atmosphere. Line 17 is encased in an expansion joint 23 located in the wall of outer sphere 11 to allow for the expansion and contraction of line 17. The gas passing through line 18 is warmed through heat exchanger 19 before it passes through filter 21 and into annulus 16. The pressure P is therefore equal on either side of the walls of the inner sphere and consequently the thickness of inner sphere 1.3 is determined with sole regard to P The thickness of outer sphere 12 is designed to withstand pressure P and the weight of inner sphere 13.

Connected to the end of line 17 terminating in annulus 16 is conduit 18. Conduit 18 circumscribes the inner sphere 13 and has a sufficient number of orifices to facilitate the distribution of vapor throughout the annulus so that the pressure acting on the outer surface of the 3 inner sphere will be substantially uniform throughout. The orifices in conduit 18 are small enough to prohibit the entrance of insulation 22 into the conduit 18.

In the preferred embodiment of the present invention, it is desired, for example, that liquid nitrogen be stored in a tank having a 32' diameter inner sphere at a ullage pressure of 325 psi. The inner sphere is stainless steel having a thickness of A" throughout except for the support course which would be slightly thicker. Approximately 34,000 pounds of stainless steel is required. The outer sphere is A516 Grade 70 type carbon steel of a uniform thickness of 2", there being approximately 400,000 pounds of the material. The annulus is 3 wide and is filled with perlite type insulating material.

The conduit through which the vapor is distributed into the annulus consists of a spiral wire encased in a tubular fabric skin which in turn is wrapped with approximately 1" of fiberglass which acts as a filter to prevent the passage of perlite while allowing the vapor to pass to and from the annulus. A similar type conduit is now marketed and is commonly referred to as a spiratube filter. A sufficient amount of said conduit is used to distribute the vapor evenly throughout the annulus.

As a further precaution, a sintered bronze filter may be installed in the line to prevent contamination of the stored material.

In an alternative embodiment of the present invention and referring now to FIGURE 2 in the drawings, the line 27 from ullage space U passes through annulus 28 and outer sphere 29 to heat exchanger 31. Line 32 from the heat exchanger 31 encloses line 27 and extends into the annulus where it joins conduit 33. Line 27 and line 32 pass through expansion joints in outer sphere 29 so that the expansion and contraction of lines 27 and 32 will not damage the outer sphere and create a leak therein.

The preceding description is presented for purposes of illustration only, it being understood that those skilled in the art will make obvious modifications while remaining within the scope and spirit of the present invention.

-What is claimed is:

1. A vessel for the storage of liquid cryogens, said liquid having a superimposed ullage pressure thereon, said vessel comprising:

an inner sphere containing the liquid and a ullage.

space, said inner sphere having wall means of a thickness sufficient to support forces less than the resulting force of the weight of the liquid and said ullage pressure;

an outer sphere enclosing said inner sphere and defining an annulus therebetween, said outer sphere having wall means of sufficient thickness to support the weight of the inner sphere and a pressure in said annulus exceeding ambient pressure; and,

means for maintaining the pressure in said annulus at a pressure exceeding ambient pressure.

2. A vessel for the storage of liquid cryogens, said liquid having a superimposed ullage pressure thereon, said vessel comprising:

an inner sphere containing the liquid and a ullage space, said inner sphere having wall means of a thickness sufiicient to support forces limited to those created by the weight of the liquid;

an outer sphere enclosing said inner sphere, said outer sphere having Wall means of a thickness sufiicient to support the weight of the inner sphere and said superimposed ullage pressure, said inner sphere and said outer sphere defining an annulus therebetwee'n; and,

means for maintaining the pressure in said annulus at substantially the same pressure as the ullage pressure.

3. The vessel described in claim 2 including means 4 for withdrawing and warming vapor from said ullage space and delivering the same to said annulus.

4. A vessel for the storage of liquid cryogens, said liquid having a superimposed ullage pressure thereon, said vessel comprising:

an inner sphere containing the liquid and a ullage space, said inner sphere having wall means of a thickness sufiicient to support forces limited to those created by the weight of the liquid;

an outer sphere enclosing said inner sphere, said outer sphere having wall means of a thickness sufiioient to support the weight of the inner sphere and said superimposed ullage pressure, said inner sphere and said outer sphere defining an annulus therebetween,

said annulus substantially filled with a granular insulating material;

a line extending from the ullage space to said annulus;

and,

a conduit extending from said line throughout said annulus, said conduit of sufficient porosity to transmit vapor from said ullage space into said annulus while restricting the entry of said granular insulating material into said inner sphere.

5. The vessel described in claim 4 wherein said line extending from said ullage space to said annulus includes means for warming said vapor to substantially ambient temperature.

6. A method for storing liquid cryogens having a superimposed ullage pressure thereon said method comprising:

providing an inner sphere for containing said liquid and a ullage space, said inner sphere having walls of a thickness sufiicient to support forces less than the resulting forces of the weight of the liquid and the ullage pressure;

providing an outer sphere to enclose said inner sphere thereby defining an annulus between said outer sphere and said inner sphere, the outer sphere having walls of sufiicient thickness to support the weight of the inner sphere and a pressure in said annulus exceeding ambient pressure; and,

providing means for maintaining the pressure in said annulus at a pressure exceeding the ambient pressure.

7. A method for storing liquid cryogens having a superimposed ullage pressure thereon said method comprising:

providing an inner sphere to contain said liquid and a ullage space said inner sphere having walls of a thickness sufiicient to support forces limited to those created by the weight of said liquid; providing an outer sphere enclosing said inner sphere,

said outer sphere having walls of a thickness sufiioient to support the weight of the inner sphere and said superimposed ullage pressure the inner sphere and the outer sphere defining an annulus therebetween; and providing means for maintaining the pressure in said annulus at substantially the same pressure as the ullage pressure.

References Cited UNITED STATES PATENTS 1,876,047 9/1932 Edmonds 62-50 2,927,437 3/ 1960 Rae 6253 2,986,891 6/1961 McMahon 6250 3,159,005 12/1964 Reed et al. 62--45 1,363,313 12/1920 Conover 62--50 2,707,377 5/1955 Morrison 6250 MEYER PERLIN, Primary Examiner.

Disclaimer 3,406,526.DudZeg T. Lush, Westmont, Ill. DOUBLE \VALLED CRYO- GEN IC VESSEL. Patent dated Oct. 2:2, 1968. Disclaimer filed Nov. 12, 1971, by the assignee, Chicago Bridge c6 Iron 00. Hereby enters this disclaimer to claims 1, 2, 3, 6 and 7 of said patent.

[Ofiicz'al Gazette February 29, 1.972.] 

